UPSC Prelims 2010 Q58: Science & Technology – Biotechnology & Genetics
- (a) They convert atmospheric methane into ammonia which the crop plants can absorb readily.
- (b) They induce the crop plants to produce the enzymes which help convert atmospheric nitrogen to nitrates.
- (c) They have the mechanism to convert atmospheric nitrogen into a form that the crop plants can absorb readily.
- (d) They induce the roots of the crop plants to absorb the soil nitrates in larger quantities.
Answer: (c) They have the mechanism to convert atmospheric nitrogen into a form that the crop plants can absorb readily.
Explanation
Why blue-green algae work as bio-fertilizers
Blue-green algae (cyanobacteria) have a special biochemical capability that benefits crop nutrition.
| Option | Verdict | Reason |
|---|---|---|
| (a) Convert atmospheric methane into ammonia | Incorrect | This describes an unrelated, incorrect biochemical process |
| (b) Induce crop plants to produce nitrogen-fixing enzymes | Incorrect | The algae themselves, not the crop plants, perform nitrogen fixation |
| (c) Convert atmospheric nitrogen into a usable form | Correct | Certain blue-green algae (cyanobacteria) possess the nitrogen-fixation mechanism, converting atmospheric N2 into ammonia/nitrates that crop plants can readily absorb |
| (d) Induce roots to absorb more soil nitrates | Incorrect | This misdescribes the algae's actual mechanism, which is fixing atmospheric nitrogen, not boosting root nitrate uptake |
Blue-green algae as bio-fertilizers:
| Point | Detail |
|---|---|
| Mechanism | Biological nitrogen fixation |
| Converts | Atmospheric N2 → plant-usable nitrogen forms |
| Common use | Paddy fields, where cyanobacteria thrive |
Answer: (c) They have the mechanism to convert atmospheric nitrogen into a form that the crop plants can absorb readily.
Why each option is right or wrong
- (a) Incorrect. Methane-to-ammonia conversion is not the real mechanism involved.
- (b) Incorrect. The algae themselves fix nitrogen; they don't merely induce the crop plant's own enzymes.
- (c) CORRECT. Blue-green algae directly fix atmospheric nitrogen into a usable form for crop plants.
- (d) Incorrect. This describes root nitrate absorption, not the algae's actual nitrogen-fixation mechanism.
Key point
Blue-green algae (cyanobacteria) work as bio-fertilizers because they can FIX ATMOSPHERIC NITROGEN directly into a form crop plants can readily absorb — not by changing crop plant enzymes or methane chemistry.
Remember
Blue-green algae as bio-fertilizer: directly fix atmospheric nitrogen into a form crop plants can readily absorb.
Common mistakes
- Confusing who performs nitrogen fixation — it's the algae itself, not an induced change in the crop plant.
- Mixing up nitrogen fixation with unrelated chemical conversions like methane-to-ammonia.
- Not connecting blue-green algae's bio-fertilizer role specifically to paddy field cultivation.
Exam tip
Blue-green algae = natural nitrogen-fixers, converting atmospheric N2 directly into usable nitrogen for crops. A core biofertilizer mechanism fact.
Sources
- NCERT Class XII Biology — Microbes in Human Welfare (biofertilisers: cyanobacteria)
- Ministry of Agriculture, Government of India — National Project on Development and Use of Biofertilizers: guidelines